Multi-scale interphase construction of self-assembly naphthalenediimide/multi-wall carbon nanotube and enhanced interfacial properties of high-modulus carbon fiber composites

Amino terminated and pi-conjugate naphthalenediimide (NDI) was designed and novel interphase with self-assembled NDI/multi-wall carbon nanotube (MWNT) was constructed on high-modulus carbon fiber (HMCF) surface, and the interfacial properties and reinforcing mechanisms of HMCF composites with various interphase were investigated. The nanoscale stiffening interphase with intertwined MWNT and flat ensiform nanostructure from NDI self-assembly were observed on MWNT@HMCF and NDI@HMCF surface, while multi-scale stiffening interphase with oblique ensiform nanostructure was constructed on NDI/MWNT@HMCF surface which was based on NDI self-assembly under confinement constraint of MWNT substrate. Compared to Pristine HMCF and MWNT@HMCF composites, the TFBT strength and IFSS of NDI@HMCF and NDI/MWNT@HMCF composites were improved by effective buffered load from stiffened interphase and smooth transition of modulus between carbon fiber and epoxy matrix. The schematic models of interphase reinforcing mechanisms were proposed as bulk failure in NDI@HMCF composite and cohesive failure in NDI/MWNT@HMCF composite, which were attributed to the shift of stress concentration and crack propagation from HMCF surface toward modulus platforms amongst nanoscale and multi-scale stiffening interphase.